1. Field of the Invention
The present invention relates to an apparatus and method for the manufacture of an article having a formed cavity adapted for filling with a fluid and subsequently sealed. More particularly, the present invention is directed to an apparatus and method for employing continuous twin thermoplastic webs to thermoform, fill, and seal a cavity for the manufacture of various useful articles and the packaging of consumer products.
2. Description of the Prior Art
The present invention primarily resulted from a search for a means to manufacture cost effective shock absorbing and load distributing articles for various applications, especially in the athletic footwear and medical fields. Such articles have been found useful in solving the problems created by impact loads generated during running or walking, as well as the problems encountered as a result of the concentrated loads suffered by ambulatory medical patients and those using prosthetic devices.
Running or jumping, especially during activities such as aerobics or basketball, creates very high localized loading of the human foot and ankle areas. This loading can contribute to injury of the foot, ankle and associated joints such as the hip and knee joints as well as various bones of the leg. Consequently, innovations in footwear products have rapidly developed in an effort to alleviate the problems associated with distributing the loads. These innovations typically relate to the introduction of comfort and fit improvements in athletic footwear which more evenly distribute the loads.
Additionally, efforts to relieve the discomfort and localized injury caused by bedridden medical patients and those using load-bearing artificial limbs have focused on the distribution of forces to improve comfort and fit.
Typical solutions to these problems included the use of ampules or pads constructed of flexible outer membranes hermetically filled with a liquid or a gas such as air. These devices were then inserted into the footwear or medical appliance at locations experiencing the greatest loading. Various membrane materials and associated manufacturing techniques have been employed, as well as a wide range of fillers.
Prior to the improvement of the present invention, a cavity useful for such ampules or pads was manufactured by welding two polymer sheets at locations defining the periphery of the filled portion of the finished article to form an enclosed two-dimensional pocket. This pocket was then individually filled with the desired fluid, such as a gas or liquid, under pressure to inflate the pocket and thus create an article having three dimensions. The fill port was then sealed to finish the article. With the cavity merely being an inflated pocket, it was not readily possible to obtain certain complex shapes adaptable for application to many shock absorbing and load distributing articles, as well as other articles useful for other applications. Further, the inflation pressures were limited by the material used. Moreover, as this process was limited to the inflation of single units, the economies of this process were not particularly suited to mass-produced articles. Also, blow molding technologies were found likewise unsatisfactory, as these technologies also require the time-consuming process of individually filling and sealing the articles.
The prior applications of thermoforming articles were also found inappropriate to form, fill, and seal a cavity for the manufacture of various useful articles and the packaging of consumer products. Thermoforming generally to date includes single sheet, twin sheet, or continuous single web thermoforming or vacuum forming techniques. In single sheet manufacture, the sheet was formed to the desired shape, typically after being heated to a formable temperature through ovens placed near the form molds. At an appropriate temperature, a vacuum was applied to the cavity of the mold drawing the formable sheet into the mold to form the cavity of the article. If a filler material or liquid was desired within the formed cavity, a separate sheet of thermoplastic or foil, such as lid stock, was subsequently placed over the formed and filled cavity and later sealed. Importantly, it was found difficult, and in most cases impossible, to completely fill the cavity through this process. Moreover, if an upper cavity was desired, a separately molded and bonded sheet was necessary.
Twin sheet thermoforming, a very narrowly applied technology, use the technique of thermoforming specifically for the purpose of entrapping air at atmospheric pressures between two relatively thick (typically, greater than 0.060 inch) pre-cut polymer sheets simultaneously formed to the desired shape after being heated to a formable temperature. After appropriate temperatures were obtained, a vacuum was applied to the cavity of the opposing molds, drawing the formable sheets into the molds to simultaneously form both portions of the article. As the still-heated sheets were formed together, a seal could be provided to bond the sheets at desired locations. This technique has not been found applicable for subsequently filling the voids created therein with a fluid. A common example of this limited forming technique is an insulating cooler, having an outer shell and an inner shell and encapsulated air therebetween as an insulating barrier. A separate top lid is generally provided to enclose the cooler.
In the case of continuous single web thermoforming techniques, a single thin thermoplastic web (typically 0.015 inch thick) is fed into a forming station, usually after being heated previously by an oven. The web is stopped near the molds, where a vacuum is applied to the cavity of the mold to draw the formable web portion into the mold to form the article. After forming and cooling, the molded portion is die cut from the web and the article(s) made from this single molded portion of the web can then be separated from the sheet. An example of products manufactured in this manner can be found in certain types of hamburger packaging boxes.
An example of a manufacturer of equipment for single web thermoforming is Brown Machine, of Midland, Mich. These thermoforming systems used a needle-driven conveyer system for the thin stock webs typically employed. In these systems, the needles puncture an edge of the web in a manner similar to that of computer printout paper drive mechanisms to transport the web. However, such machines were found to be of little use in the manufacture of articles such as the shock attenuating and/or load distributing articles as herein disclosed, as well as other useful articles and the packaging of consumer products according to the present invention.
One important drawback is that the web, unlike computer paper, does not have pre-punched holes for engagement by the needles. In the case of hard or elastomeric polymers (e.g., polyurethane), it has been found that the needles often do not properly puncture the edge of the web. Without proper punctures, the webs often would fall off of the conveyor system onto the ovens and create a fire hazard. Also, importantly in the context of the present invention, these needle driven systems are incapable of maintaining a suspended web against gravity where one of the conveyors is inverted to transport the upper web of a twin web thermoforming system. Thus, in the development of the present invention, it was recognized that the prior art systems using needle drive conveyers were not appropriate in the fabrication of articles having fluid filled cavities and requiring a thicker membrane thickness.
Alternatively, the molds themselves have been used to transport the web. However, given the extensive costs for an individual mold (e.g., $8,000), this transport system was not considered cost effective for the present multi-mold applications contemplated, such as the various useful articles herein disclosed and other packaging of consumer products.
Other form, fill, and seal apparatus vendors, such as Klochner, located in Florida, provide chain-driven web feeding conveyer systems. These systems, however, have never been applied to conventional thermoforming or twin web form, fill, and seal applications. They allow the transport of webs which are generally not transportable by the needles of the needle drive conveyors described above. These systems are typically used where very accurate registration is needed. Further, these systems are typically used where very thin low density polyester films (e.i., rigid polyvinylcloride films) and other films having limited stretch characteristics and tend to tear when needle driven. These systems are also typically used for packaging applications employing very thin (e.g., 0.015 inch) co-extruded films. However, such systems have never been applied to twin sheet or conventional thermoforming due to the typically thinner web thickness used in these applications.
In developing the apparatus and method of the present invention, filler liquids for their application to shock attenuating devices including included water, glycol mixtures, various oils and other liquids of relatively low viscosity were employed. Other viscosity liquids or gels, in an effort to improve the hydrostatic properties of the liquid, have incorporated semi-solids such as organosiloxane gels as the shock absorbing or load distributing material. Gas fillers have typically employed enclosed pockets of air. Whereas in the past these devices used liquids, gels, or air, depending on the desired viscosity, none apparently offered the cost effective shock attenuation and load distribution properties of articles fabricated according to the invention disclosed and claimed in the aforementioned parent patent application, which use a mixture of super absorbent materials and a liquid as the filler material.
Super absorbent materials have long been used to absorb various liquids for ready and efficient disposal in articles such as diapers, sanitary napkins, bedding pads and the like. These super absorbent materials, uniquely suited to such applications, are generally hydrophilic and absorb an enormous quantity of liquid relative to their mass through capillary action.
Improvements were generally sought to provide and produce shock attenuating and load distributing devices of high durability, low cost, and which are readily manufactured for use in footwear, medical applications and other areas where the dissipation of load over time and/or an area is desired. To this end, the feasibility of fabricating an article using super absorbent materials, in combination with an appropriate liquid, to form a low cost viscous colloidal fluid as the shock attenuating and load distribution material encapsulated in an articulable article, was sought.
Thus, in one application, the apparatus and method of the present invention can be applied to the manufacture of an improved shock attenuating and/or load distributing articles, wherein a load distributing material as a viscous colloidal fluid obtained from a combination of super absorbent material and a liquid, such as water, is injected into a vacuum-formed cavity through an injection port, which is subsequently sealed.
Importantly, however, the application of the present invention can be used for the manufacture of a wide range of different products which may be thermoformed, filled, and sealed, such as in food-stuff packaging and fluid filled consumer products (e.g., shampoo containers).